It is known that red phosphorus undergoes a chemical reaction upon storage in a moist atmosphere to form phosphine and various acids of phosphorus, mainly phosphorous acid and phosphoric acid. The formation of the highly toxic phosphine gives rise to hazardous working conditions and unpleasant odours and the formation of the phosphorous and phosphoric acids is undesirable in end uses of red phosphorus. Aluminum in the form of its hydroxide has been widely used to stabilize red phosphorus against such degradation. However, relatively large amounts of aluminum are required to achieve a significant degree of stabilization.
An additional problem which arises with the prior art aluminum treatment is that the product is difficult to process. A layer of alumina is precipitated onto the red phosphorus particles in an aqueous dispersion thereof and the treated red phosphorus is filtered and dried. Efficient filtration of the treated red phosphorus is difficult to achieve as a result of gelation of the aluminum hydroxide and large quantities of water are retained by the aluminum hydroxide.
More recently, as described in my copending U.S. patent application Ser. No. 396,125 filed July 7, 1982 (now U.S. Pat. No. 4,421,728), it has been found that stabilization of red phosphorus can be achieved using titanium dioxide or titanium phosphate in lesser quantities than required for aluminum hydroxide treatment and further that the treated red phosphorus is readily and rapidly filtered. Another advantage of the titania-treated red phosphorus is that it may be heated at elevated temperatures up to 300.degree. C. without the evolution of water, so that the product is suitable for addition to plastics which are processed at high temperatures.
It has also been suggested in Canadian Pat. No. 1,097,152 to stabilize red phosphorus against oxidation by superficially covering each red phosphorus particle with a thin film of a hardened melamine-formaldehyde resin.
It further has been suggested in U.S. Pat. No. 4,315,897 to stabilize red phosphorus against oxidation by the simultaneous treatment of red phosphorus particles by aluminum hydroxide and hardened epoxy resin.